JP2008533727A - Method for processing an object, in particular a method and an apparatus for cleaning semiconductor elements - Google Patents

Abstract

The present invention relates to the continuous cleaning of an object, particularly a semiconductor element, using ultrasonic waves, and the object to be cleaned is disposed in a liquid. The invention further relates to an apparatus for carrying out the method according to the invention. The basic concept of the present invention is that the surface of an object to be cleaned (2) in a tank (5) filled with liquid is at least one vibration maximum generated by at least one sound source (8a) in the tank (5). To pass the point. According to one embodiment, the sound source field (8) located in the tank (5) is arranged inclined with respect to the transport direction (4).
[Selection] Figure 1

Description

  The present invention relates to cleaning an object, particularly a semiconductor element, using ultrasonic waves, and the object to be cleaned is disposed in a liquid. The invention further relates to an apparatus for carrying out the method according to the invention.

  In general, cleaning using ultrasonic waves is well known. Ultrasonic cleaning is mainly used in industrial parts manufacturing, especially in electrical engineering, precision mechanics, metalworking, or circuit board manufacturing. Other typical fields of application for cleaning this type of object can be found in the optical industry as well as in medical technology. The use of ultrasound is particularly useful for removing contaminant particles from an object, for example when a mechanical cleaning device such as a brush or abrasive means reaches the impurities and is insufficient to remove it. It is proposed.

  For ultrasonic cleaning by methods known in the art as well as by the method of the present invention, sound waves emitted from an ultrasonic generator using a suitable ultrasonic transducer are applied to the object to be cleaned via the liquid medium. The object to be cleaned needs to be placed in the liquid so that it can be sent. A so-called sound source field emits a sound wave that strikes the object to be cleaned.

  In particular, different cleaning steps are required during the semiconductor manufacturing process to remove contaminant particles as well as particles formed from the semiconductor, for example from a wafer or disk, during processing. In particular, these particles generated from mechanical processing of the semiconductor element (substrate), such as cutting, are cutting particles made of the material of the substrate. Also, so-called “slurries”, or abrasive powder emulsions, are often used. This slurry includes silicon carbide or aluminum oxide in a mixture containing glycol or oil. These impurities (fine powder, particles, organic compound residues, etc.) must be removed in one or several washing steps in order to ensure the required product properties.

  In the method known from the prior art, first, an object to be cleaned, for example a wafer or a disk, is sorted into a carrier. Subsequently, they are manually or automatically submerged in a tank containing a suitable liquid and the carrier is placed or alternatively moved through the wash tank either by an operating system or manually.

  In order to obtain good cleaning results, several different tanks with different liquids and / or different sound sources are generally provided, for example 10 to 20 tanks. Since the sound source itself emits different frequencies, different cleaning results are produced in the individual tanks.

  To assist the cleaning effect, the tank is generally operated warm and the temperature is usually adjusted between 30 ° C and 60 ° C. The frequency is in the ultrasonic region and is typically emitted by a sound source located at the bottom of the wash tank and partially on its inner wall. As another method or in addition to this, a so-called underwater vibrator is used, which is preferably arranged at a position where it is desired to make the distribution of sound waves in the cleaning tank as uniform as possible. In another preferred method of the prior art, the underwater vibrator is provided as a flat plate vibrator, and in many cases is disposed below the object to be cleaned. The plate vibrator is usually used for a component having a large area to ensure that the sound wave reaches the entire object.

  The total time for such a cleaning process, including drying, typically reaches about one hour, often requiring several manual or mechanically assisted transfer steps, resulting in a failure rate. Is relatively high. For this reason, there is a need for an alternative cleaning method that can handle objects to be cleaned more quickly, cheaply and carefully, especially when processing future wafers with edge lengths of 200 mm and widths below 200 μm. It is.

  U.S. Pat. No. 4,979,994 B discloses a method and apparatus for cleaning a printed circuit board, where the printed circuit board is treated with sound waves in a liquid. In order to ensure cleaning even in the space between the electrical component and the printed circuit board, the direction of the sound source field is inclined, that is, from −60 degrees to +60 degrees toward the vertical line of the printed circuit board. It is inclined by the angle between. Also, these undercuts are reached by reflection. Individual sound source fields and printed circuit boards irradiated with sound waves remain stationary relative to each other.

  DE-C 1 078 406 discloses an apparatus for cleaning metals by ultrasound. The device consists of a rotating drum in the shape of a funnel. The position of the sound source field can be adjusted along the peripheral surface of the drum and is fixed.

  DE 192 22 423 C2 discloses an apparatus for processing substrates, in particular semiconductor wafers. These substrates are mounted on rod-shaped carrier elements in the fluid tank. To improve the cleaning yield, the carrier element with the substrate can be raised and lowered, and the distance from the sound source field to the substrate can be arbitrarily increased or decreased.

  An object of the present invention is to provide a method and / or apparatus for cleaning particularly fragile objects using sound waves.

  The basic concept of the present invention is to provide a method and apparatus designed to ensure that at least one vibration maximum point strikes the surface of the object to be cleaned in the cleaning tank, said vibration maximum point being in the tank. Emitted by at least one sound source. This vibration maximum point corresponds to a so-called antinode.

  Thus, a method according to claim 1 and / or an apparatus according to claim 2 is provided.

  According to the present invention, the aspect can be realized by using various means described below. A characteristic common to these alternative embodiments is that each vibration maximum point having a maximum amplitude hits the object to be cleaned. For this purpose, it is necessary to adjust the mechanical distance between the sound source and the object to be processed to an accuracy of several millimeters. Such application of ultrasonic waves to the liquid in the cleaning tank is optimized with respect to the prior art, and is similarly ensured in all embodiments.

  The wavelength λ of the ultrasonic wave in the liquid is typically from 10 mm to 80 mm, the frequency is from 20 kHz to 132 kHz, and the liquid is water. (For example, for a frequency of 25 kHz, the wavelength in water is about 59 mm.)

  The sound source is preferably made as a so-called sound source field. In the following, the term sound source field refers to a device consisting of several vibration sources that emit at least themselves in phase. In particular, such a sound source field can be a flat plate vibrator having a planar surface.

  In addition to eliminating the disadvantages of the prior art as described above, an important advantage of the present invention according to the preferred embodiment is that the cleaning of objects requires manual or automatic repositioning or re-sorting. It can be executed continuously.

  According to the present invention, this can be beneficially achieved by transporting the object to be cleaned through the liquid by the transport device. An example of such a transport system is disclosed in WO2003 / 086913 A1. During its transport, the object passes along a series of differently tuned sound sources, which are located in the cleaning liquid and emit frequencies in the ultrasonic region. The precise spatial correlation between the sound source field and the surface of the object to be cleaned realized in an alternative embodiment ensures that sound waves strike the object to be cleaned at their vibration maximum. This can be achieved directly or indirectly as shown below.

  Mechanically, the sound source field can be placed at a defined distance from the object to be cleaned in a tank filled with liquid.

  However, the liquid composition and temperature, as well as the reflections that can occur on the object to be cleaned, as well as other internal components provided in the tank, will usually make a difference, which will displace the predetermined antinode. For this reason, there is an uncertainty that it is not possible to guarantee that at least one antinode of the sound wave hits the object to be cleaned with the maximum amplitude in spite of optimal mechanical conditions.

  In the first aspect of the present invention, it is preferable that the individual sound source fields pass through the object to be cleaned by the conveying device along the same, but are not arranged parallel to the conveying direction but are inclined. In this case, the term “inclined” means that the sound source field is not oriented parallel to the surface defined by the object to be cleaned together with the surface, and the specified inclination angle is between the surface of the sound source field and the surface of the object to be cleaned. It means that it exists. Here, the tilt angle is independent of the transport direction. This means that the tilt angle may be along the transport direction, that is, the distance from the sound source field to the surface of the transported object is increased or vice versa.

  According to the present invention, in a continuous embodiment, it is proposed that two or more sound source fields are arranged while an object is transported through the tank. These may be driven by different frequencies. The individual sound source fields driven by the same frequency are preferably separated from one another by tank separators. It is suggested to start at a low frequency (eg, 25 kHz) to remove coarse and large particles at the beginning of the first cleaning step. Depending on the actual characteristics of the work, it is preferable to gradually increase the frequency in the conveying direction (for example, 40 kHz or more), and this allows continuous coarse particles to fine particles from the start region to the end region. Removed. These frequencies extend to the mega sound band, and the mega sound band uses frequencies from 800 kHz to 2 MHz. Here, in addition to the distance to the transport surface of the object to be cleaned in each sound source field, it is possible to change the inclination angle thereof.

  In order to obtain a good cleaning result and to solve the problem of hitting an object passing at least one vibration maximum point along the sound source field, in the present invention, the inclination angle of the sound source field with respect to the conveying surface of the object is λ. We propose to be surely smaller than / 2. Here, λ is the wavelength emitted by the sound source field. It has been found useful to adjust the theoretical position of the antinodes above the center of the vibration region to incline the entire sound source field to a value that is reliably smaller than λ / 2. Even when the angle of inclination of the sound source field with respect to the conveying surface of the object is λ / 4 or λ / 8, a very effective cleaning result can be obtained. When the sound source fields are arranged in parallel, the inclination angle of the sound source field is provided as an alternative, if necessary, by arranging a focusing reflection surface between the field and the object to be processed so that the sound wave exhibits the above-mentioned propagation characteristics. Can be obtained. Another alternative embodiment with a horizontally oriented sound source field is to move the object to be cleaned at least temporarily from a horizontal position to a tilt angle.

  In another embodiment, the tilted sound source field is guided at least partially parallel to the transport plane and thereby moved in the transport direction.

  In another aspect of the present invention, the above inventive principle is that the sound source field is disposed horizontally and parallel to the transport surface as long as the sound source field is movable and takes into account relative movement with respect to the object. This can also be realized. Actually, since the position of the sound source field oriented horizontally with respect to the object to be cleaned can be changed, the antinode of the sound wave hits the object to be processed at a maximum amplitude once in the movement path.

  For this reason, in a preferred embodiment, the sound source field is movable and arranged parallel to the transport direction of the object to be cleaned, this movement being performed perpendicularly (vertically) to the transport direction.

  In order to achieve a more uniform cleaning, it is advantageous that the movement according to another embodiment is performed vertically (vertically) and horizontally (parallel) in the transport direction, and this vertical and horizontal movement is continuous. Or at the same time.

  In another embodiment, a combination of the embodiments disclosed above is provided. This means that a three-dimensional movement of the sound source field occurs. In a preferred combination, the sound source field is movable, for example, and is inclined with respect to the conveying direction of the object to be cleaned, and this movement is performed perpendicularly or perpendicularly and horizontally to the conveying direction. . Even by this combination method, at least one vibration maximum point reliably strikes the object to be cleaned.

  In the embodiment of the present invention already mentioned, the sound source field is moved relative to the object to be cleaned in parallel with the transport direction or the transport surface. In order to establish a stable sound field as much as possible, It is beneficial to perform the relative movement slowly. Here, the amplitude perpendicular to the conveying direction is typically surely smaller than λ / 2, where λ is the wavelength emitted by the sound source field. In a particularly preferred embodiment, the amplitude measured perpendicular to the transport direction is λ / 4. While the object to be cleaned is in the tank, it is necessary to pass this amplitude at least once.

  In an embodiment of the invention, the object is placed in a transport device, for example a rotary transport system. Here, the object is transported by several transport rollers arranged one after another and oriented horizontally. The individual transport rollers are arranged in the fluid such that the respective upper ends of the rollers are located approximately at the level of the fluid surface, i.e. the upper boundary of the fluid, so that the lower surface of the individual object is directly in contact with the fluid surface. Soaked in contact. Here, a meniscus is formed at the end of the object. Thus, the interaction between gravity and surface tension pulls the object down and keeps the object in contact with the roller without causing it to float. Thereby, the roller transport system can control and define the object to be transported.

  In a particularly preferred embodiment, the transport roller comprises at least two support elements, which are advantageously arranged in the area of the two grooves of the transport roller. The distance between the support elements is determined by the width of the object to be processed. In the area of the sound source field, it is strongly required that the object to be cleaned has a sufficient space. For this reason, the guide elements are further spaced apart, especially in this region, and the depressing means arranged on the opposite side of the conveying roller and surrounding the object to be cleaned has a great degree of freedom of movement, thus diverting possible forces from the object. be able to. Thus, the object can be achieved by minimizing the force applied to the item to be cleaned. In this way, the breakage rate is greatly reduced.

  The transport roller is preferably composed of at least two parts and comprises a spindle element and at least one track element surrounding the spindle element. In the area of the sound source field, the spindle elements of the individual transport rollers are further spaced from each other, so that the sound wave emitted from the sound source field strikes the object to be cleaned even better. The spindle is made of a material that impedes the propagating sound wave only slightly.

  In another aspect of the invention, an apparatus for carrying out the method according to the invention is provided. The important characteristics of this device arise from the above information on process control and are summarized in claim 2.

  The implementation of the method according to the invention results in a significant reduction in processing time compared to the known methods, in addition to the advantages already mentioned. The present invention proves that the typical processing time of about one hour can be reduced to about 10 minutes.

  Another important advantage of the present invention is that implementing the method according to the present invention eliminates the sharing of chemicals in the cleaning bath. Furthermore, the present invention allows the temperature of the cleaning solution to be adjusted to room temperature, that is, from about 15 ° C. to 25 ° C., without having to worry about the significant deterioration in cleaning results achieved by the present invention.

  In alternative methods, water from which minerals have been partially removed or water from which ions have been partially removed can be used as the cleaning medium.

  However, this context clearly indicates that the present invention naturally includes the application of a common temperature and / or the use of chemical agents in the cleaning solution.

  Further advantages result from the following description, drawings and claims.

  FIG. 1 shows an overview of an apparatus 1 for cleaning an object 2, in particular a disc-shaped wafer, according to the invention.

  The object 2 is moved in the transport direction 4 through the tank 5 by the transport device 3. The tank 5 is filled with the liquid 6. The conveying device 3 itself is preferably composed of a driving roller 3a and a push-down means 3b (FIG. 2), and the driving roller 3a rotates in the direction of the arrow 7, so that it is useful for driving the object 2 in the conveying direction 4. Is. The push-down means 3b that rotates in the reverse direction serves to ensure that the object 2 does not float in the liquid 6.

  The tank 5 is divided into different areas, so-called segments 5a, 5b, 5c. The segments 5 a, 5 b and 5 c are all fluidly connected to each other and are used via the transport device 3. For the exemplary embodiment shown here, at least one sound field 8 is arranged in each segment 5a, 5b, 5c. The sound source field 8 emits sound waves 8b from the sound source 8a in the direction of each object 2 arranged above the sound source field. A sound wave generated by the sound source field 8 is applied to the liquid by the liquid 6 surrounding each sound source field 8 and sent to the object 2.

  In another exemplary embodiment, although not shown in detail, it is also possible to place one or more sound source fields 8 in a segment.

  The segments 5a, 5b, 5c are not necessarily required for carrying out the method according to the invention and for the device. They merely serve to more easily reveal individual areas and to detail different cleaning areas. In the present invention, the number of segments shown is not fixed, and can be freely selected in consideration of actual requirements.

  The sound source field 8 is arranged in the segments 5a, 5b, and 5c so as not to be parallel to the transport direction 4, and indicates an inclination. This means that they are arranged inclined with respect to the conveying direction 4, and the principle of the inclination is arranged in both directions (along the conveying direction or vice versa, respectively). Due to this inclined arrangement, an angle α is formed between the horizontal plane 9 in the conveying direction 4 and the plane 10 of each sound source field 8. The specified tilt angle is preferably smaller than λ / 2, where λ is the wavelength at which the sound wave generated by the sound source field 8 is emitted.

  In this illustrative embodiment, the sound source field 8 is placed in the individual segments 5a, 5b, 5c.

Method Here, by way of example, individual objects 2 in the form of flat, ie flat wafers, are each sent to the first sector A of the transfer device 3 (ie delivered from another processing step) and transferred to the transfer device. 3 (in addition to the push-down means 3b, the transport roller 3a) is moved in the transport direction 4. After a suitable start-up phase, the object to be cleaned 2 reaches the first sector 5 a and passes over the first sound source field 8. While passing over the sound source field 8 according to the invention, the arrangement of the sound source field 8 causes at least one antinode to hit the surface of the object with maximum amplitude. Continuously, the object 2 is conveyed from this segment 5a to the next segment 5b and the like. The process is repeated above each sound source field 8.

  For the method and device 1 shown here, individual sound source fields 8 are arranged in individual segments 5a, 5b, 5c, and the frequency in the device according to the invention is stepped from one sound source field 8 to the next sound source field 8. And it is preferable to arrange | position so that it may increase linearly. At the end E of the device according to the invention, the cleaned object that has been treated in a continuous process is lowered and transferred to another facility.

1 shows a schematic view of an apparatus for cleaning an object, in particular an apparatus for cleaning semiconductor elements each in the form of a wafer or disk, for carrying out the method according to the invention. FIG. 1 shows a partial view of FIG. 1 and helps to clarify the conveyance of an object to be cleaned.

Explanation of symbols

1 Equipment 2 Object (Wafer)
DESCRIPTION OF SYMBOLS 3 Conveying device 3a Conveying roller 3b Pushing means 4 Conveying direction 5 Tank 5a Segment 5b Segment 5c Segment 6 Liquid 7 Arrow (rotation direction)
8 sound source field 8a sound source 8b sound wave 9 surface (transport surface, surface in the transport direction 4)
10 (sound source field 8)
A Start (first sector)
E Termination part α Angle λ Wavelength

Claims (14)

Method of processing an object in a tank (5) with a liquid (6) and a sound source field, in particular a method of cleaning a semiconductor element, wherein the object (2) is transported through the tank (5) The sound source field (8), which is continuously conveyed on the device (3) and applies the sound wave (8b) to the liquid (6), has the following positions:
I. An arrangement of the sound source field (8) placed and inclined with respect to the surface (9) in the transport direction (4) of the object to be cleaned (2);
II. An arrangement of the sound source field (8) that is movable and inclined with respect to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4 ) Arranged in parallel with
III. An arrangement of the sound source field (8) that is movable and parallel to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4) Placed vertically,
IV. An arrangement of the sound source field (8) that is movable and parallel to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4) V. a vertical and horizontal arrangement, or V. An arrangement of the sound source field (8) that is movable and inclined with respect to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4 Optionally having one of the arrangements performed vertically or vertically and horizontally. An apparatus for processing and cleaning an object (2) in a tank (5) having a liquid (6) and a sound source field, particularly an apparatus for cleaning a semiconductor element, wherein the object (2) is the tank (5). ) Through the transport device (3), and the sound source field (8) for applying the sound wave (8b) to the liquid (6) has the following position:
I. An arrangement of the sound source field (8) placed and inclined with respect to the surface (9) in the transport direction (4) of the object to be cleaned (2);
II. An arrangement of the sound source field (8) that is movable and inclined with respect to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4 ) Arranged in parallel with
III. An arrangement of the sound source field (8) that is movable and parallel to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4) Placed vertically,
IV. An arrangement of the sound source field (8) that is movable and parallel to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4) V. a vertical and horizontal arrangement, or V. An arrangement of the sound source field (8) that is movable and inclined with respect to the surface (9) in the transport direction (4) of the object to be cleaned (2), wherein the movement is in the transport direction (4 Optionally having one of the arrangements made vertically or vertically and horizontally.   The sound source field (8) is arranged so that the sound wave (8b) generated by the sound source field (8) hits the object (2) at the maximum vibration point with respect to the object to be cleaned (2). The device according to claim 2.   4. A device according to claim 3, characterized in that the sound source field (8) is tilted reliably smaller than [lambda] / 2, where [lambda] indicates the wavelength of the emitted sound wave (8b).   Device according to at least one of claims 2 to 4, characterized in that the sound source field (8) emits different frequencies.   Device according to claim 5, characterized in that the frequency emitted by the sound source field (8) increases in the transport direction (arrow 4).   The transport device (3) for loading the object (2) comprises transport elements extending perpendicularly to the transport direction (4) and arranged at a distance from each other. Item 7. The apparatus according to at least one of Items 2-6.   8. The device according to claim 2, wherein the sound source fields (8) are arranged one after another in the transport direction (4).   Device according to claim 8, characterized in that the sound source field (8) has the same tilt angle α with respect to the plane in the transport direction (4).   9. Device according to claim 8, characterized in that the sound source field (8) has a different inclination [alpha] with respect to the plane in the transport direction (4).   Device according to at least one of claims 2 to 10, characterized in that the temperature of the liquid (6) in the tank is adjusted to room temperature.   12. Device according to claim 11, characterized in that the temperature of the liquid (6) is adjusted to a value between 15 [deg.] C and 25 [deg.] C.   Transporting the transport elements further away from each other compared to the rest of the transporting device (3) for transporting the object to be cleaned (2) in the vicinity of the sound source field (8) 13. A device according to at least one of the preceding claims, characterized in that it comprises a roller.   14. A device according to at least one of claims 2 to 13, characterized in that the conveying element comprises a conveying roller and at least partly a depressing means.

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